Citrobacter spp (other)

• C. amalonaticus
• C. farmeri

• Gram negative bacilli - fermenter

Clinical Significance

These organisms are found in the environment and the gastrointestinal tract of humans and animals. 

They have been associated with bacteremia, urinary tract, skin/soft tissue, and bone and joint infections.

Usual Susceptibility Pattern

These organisms produce an inducible  chromosomal β-lactamase (CTX-M cefotaximase) resulting in intrinsic resistance to ampicillin and cephalothin.  Hyperproduction of this enzyme results in resistance to cefazolin, ceftriaxone, +/- beta-lactamase inhibitor combination drugs.  Ceftazidime may still test susceptible but should be avoided.